code: def test_plot_knee_normalized():
      """Test that plotting is functional"""
      with np.errstate(divide="ignore"):
          x = np.linspace(0.0, 1, 10)
          y = np.true_divide(-1, x + 0.1) + 5
      kl = KneeLocator(x, y, S=1.0, curve_nature="concave")
      num_figures_before = plt.gcf().number
      kl.plot_knee_normalized()
      num_figures_after = plt.gcf().number
      assert num_figures_before < num_figures_after
  
file_path: yellowbrick/tests/test_utils/test_kneed.py
imports: import pytest
  import matplotlib.pyplot
  import numpy
  from yellowbrick.utils.kneed import KneeLocator
label_desc: Use image node_id 12 for calling a global function with example usage: test_plot_knee_normalized() without return types